X-ray characterization of oriented β-tantalum films

Includes bibliographical references (pages 408-409).Tantalum (Ta) metal films (10-70 nm) were deposited on a Si(100) substrate with a 500 nm silicon dioxide (SiO2) interlayer by ion-beam assisted sputtering. The as-deposited films have been characterized by X-ray diffraction (XRD) and X-ray reflectivity (XRR) techniques. XRD measurements showed the presence of films of the tetragonal phase of tantalum (β-Ta) oriented along the (00l) plane. XRR measurements indicated the presence of graded Ta films, with a thin interface layer between the 500 nm SiO2 layer and the Ta films. The thickness and density of this interface layer was estimated to be 1.9±0.2 nm and 10.5±0.5 g/cm3, respectively. X-ray photoelectron spectroscopy (XPS) was used to probe the chemical composition of this interface layer. XPS investigative studies indicated that the interface was likely composed of tantalum silicide (TaSi2) and tantalum silicate (TaSiOx). However, the TaSiOx layer was reduced during Ar ion sputter depth profile analysis

Layered structure of room-temperature ionic liquids in microemulsions by multinuclear NMR spectroscopic studies

Microemulsions form in mixtures of polar, nonpolar, and amphiphilic molecules. Typical microemulsions employ water as the polar phase. However, microemulsions can form with a polar phase other than water, which hold promise to diversify the range of properties, and hence utility, of microemulsions. Here microemulsions formed by using a room-temperature ionic liquid (RTIL) as the polar phase were created and characterized by using multinuclear NMR spectroscopy. 1H, 11B, and 19F NMR spectroscopy was applied to explore differences between microemulsions formed by using 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as the polar phase with a cationic surfactant, benzylhexadecyldimethylammonium chloride (BHDC), and a nonionic surfactant, Triton X-100 (TX-100). NMR spectroscopy showed distinct differences in the behavior of the RTIL as the charge of the surfactant head group varies in the different microemulsion environments. Minor changes in the chemical shifts were observed for [bmim]+ and [BF 4]- in the presence of TX-100 suggesting that the surfactant and the ionic liquid are separated in the microemulsion. The large changes in spectroscopic parameters observed are consistent with microstructure formation with layering of [bmim]+ and [BF4]- and migration of Cl- within the BHDC microemulsions. Comparisons with NMR results for related ionic compounds in organic and aqueous environments as well as literature studies assisted the development of a simple organizational model for these microstructures. Confining ions: Multinuclear NMR experiments were used to explore two different reverse micelle systems formed by using a cationic and nonionic surfactant with the room-temperature ionic liquid (RTIL) [bmim][BF4] (bmim=1-butyl-3-methylimidazolium) as the polar phase. Microemulsions formed by using a cationic surfactant revealed layering of the RTIL that does not occur in systems formed with the nonionic surfactant (see figure). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Fil: Falcone, Ruben Dario. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Baruah, Bharat. Kennesaw State University; Estados Unidos. State University of Colorado - Fort Collins; Estados UnidosFil: Gaidamauskas, Ernestas. State University of Colorado - Fort Collins; Estados Unidos. Vilniaus Universitetas; LituaniaFil: Rithner, Christopher D.. State University of Colorado - Fort Collins; Estados UnidosFil: Correa, Nestor Mariano. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Silber, Juana. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Crans, Debbie C.. State University of Colorado - Fort Collins; Estados UnidosFil: Levinger, Nancy E.. State University of Colorado - Fort Collins; Estados Unido

Comparison of nanometer-thick films by x-ray reflectivity and spectroscopic ellipsometry

Includes bibliographical references (pages 023906-5).Films of tantalum pentoxide (Ta2O5) with thickness of 10-100 nm were deposited on Si wafers and have been compared using spectroscopic ellipsometry (SE) and x-ray reflectivity (XRR). (Ta2O5) was chosen for comparison work based on various criterions for material selection outlined in this article. Measurements were performed at six positions across the sample area to take into consideration thickness and composition inhomogeneity. SE and XRR fitted curves required the incorporation of a linearly graded interface layer. SE systematically measured higher values of film thickness as compared to XRR. A linear equation was established between the thickness measurements using SE and XRR. The slope of the linear equation established was found to be 1.02±0.01. However, the intercepts were found to be 1.7±0.2 and 2.6±0.3 when the interface was excluded and included, respectively. These differences in the values of intercepts were attributed to the uncertainties in the determination of the interface layer

Conformation and dynamics of the ligand shell of a water-soluble Au102 nanoparticle

Inorganic nanoparticles, stabilized by a passivating layer of organic molecules, form a versatile class of nanostructured materials with potential applications in material chemistry, nanoscale physics, nanomedicine and structural biology. While the structure of the nanoparticle core is often known to atomic precision, gaining precise structural and dynamical information on the organic layer poses a major challenge. Here we report a full assignment of 1 H and 13C NMR shifts to all ligands of a water-soluble, atomically precise, 102-atom gold nanoparticle stabilized by 44 para-mercaptobenzoic acid ligands in solution, by using a combination of multidimensional NMR methods, density functional theory calculations and molecular dynamics simulations. Molecular dynamics simulations augment the data by giving information about the ligand disorder and visualization of possible distinct ligand conformations of the most dynamic ligands. The method demonstrated here opens a way to controllable strategies for functionalization of ligated nanoparticles for applications.peerReviewe

Solution structure of the N-terminal A domain of the human voltage-gated Ca2+channel β4a subunit

Ca2+ channel β subunits regulate trafficking and gating (opening and closing) of voltage-dependent Ca2+ channel α 1 subunits. Based on primary sequence comparisons, they are thought to be modular structures composed of five domains (A–E) that are related to the large family of membrane associated guanylate-kinase (MAGUK) proteins. The crystal structures of the β subunit core, B–D, domains have recently been reported; however, very little is known about the structures of the A and E domains. The N-terminal A domain is a hypervariable region that differs among the four subtypes of Ca2+ channel β subunits (β1–β4). Furthermore, this domain undergoes alternative splicing to create multiple N-terminal structures within a given gene class that have distinct effects on gating. We have solved the solution structure of the A domain of the human β4a subunit, a splice variant that we have shown previously to have α 1 subunit subtype-specific effects on Ca2+ channel trafficking and gating

Nanoconfinement’s Dramatic Impact on Proton Exchange between Glucose and Water

Glucose nanoconfined by solubilization in water-containing AOT (sodium bis­(2-ethylhexyl) sulfosuccinate) reverse micelles has been investigated using ¹H NMR. NMR spectra reveal well-defined signals for the glucose hydroxyl groups that suggest slow chemical exchange between them and the water hydroxyl groups. Using the EXSY (ZZ-exchange) method, the chemical exchange rate from water to glucose hydroxyl groups was measured for glucose in reverse micelles as a function of size (water pool diameter of ∼1–5 nm) at 25 °C. The chemical exchange rates observed in the nanoconfined interior are dramatically slower (5–20 times) than those observed for glucose in bulk aqueous solution at the same concentration as the micelle interior. Exchange rate constants are calculated via a mechanism that accounts for these observations, and implications of these results are presented and discussed